At present, radiation CT systems such as X-ray CT systems are widely used in various medical institutions for three-dimensional imaging of the regions of interest of the subjects to assist the clinicians to achieve an accurate medical diagnosis of the subjects.
In a radiation CT system, a radiation tube generating cone-shaped radiation beams and a two-dimensional radiation area detector detecting the radiation are placed in rotation around a rotation center, wherein the two-dimensional radiation area detector is disposed opposite to the radiation tube and consists of detector elements arranged in a matrix. Projection data generated by the radiation rays transmitting through the subject are collected; based on the collected projection data, an image of the region of interest of the subject is reconstructed; and then the reconstructed CT image is displayed on an image display device.
In a radiation CT system, a collimator is generally provided between the radiation tube and the subject to be detected. By adjusting the slit width of the collimator, the width of the radiation beam in a direction parallel to the subject is controlled so as to control the thickness of the scan.
In one conventional type of collimator, the longitudinal edges of the slit thereof have a linear shape. Because the rectangular X-ray detector is usually placed in an arc surface centered on the focus of the X-ray tube, the X-ray beam projected onto the X-ray detector by using such a conventional collimator forms a projection range that has an irregular rectangular shape, thus reducing the detection accuracy and resulting in an additional dose of radiation to the subject.
Another conventional type of collimator and its slit are configured to have a curved shape, so that the arc surface where the collimator is located and the arc surface where the rectangular X-ray detector is located are both centered on the focus of the X-ray tube. Accordingly, the X-ray beam projected onto the X-ray detector by using such a conventional collimator forms a projection range that has a regular rectangular shape. However, due to limitations on the materials of the collimator, it is difficult to produce a collimator having a curved shape and the processing difficulty and cost involved are high.
At present, there is a further, plate type collimator in which the slit profile is designed by using a general formula for a CT collimator slit profile. Such a collimator can enable the X-ray beam projected onto the X-ray detector consisting of rectangular units to form a projection that is close to the profile of the X-ray detector itself, but it is still defective in that a large number of over-shoot and short-shoot areas exist.
Therefore, there is a need for a method capable of quickly and easily determining the CT collimator slit profile and a CT imaging system capable of avoiding additional radiation dose while maintaining detection accuracy.